Conventional board tracking devices rely on spraying or imprinting an identification code or symbol on each board and reading the information with a sensor after the board has traveled to a subsequent machining station. The printing and reading processes are preferably performed at high speeds and may be physically difficult to reliably achieve because of the dynamic nature of the boards themselves.
If wood is missing from an area where the board is printed, the board's identification code can be illegible to the reader. A twisted board, or one with bark or some other defect in the print zone, can also be difficult to reliably mark and identify. A board may also turn over during travel between stations, requiring that either both sides be marked, or both sides be read.
Another problem with conventional board tracking devices is that printing systems contain print media, such as ink or paint, and moving parts that contribute to decreasing reliability. Ink jet and/or spray systems require constant maintenance to keep them working properly. Most require compressed air, are adversely affected by temperature extremes, and are very sensitive to variations in the ink or paint quality. For example, unless the print media is continually circulated when the system is not in use, the print media can freeze, its pigments can separate, and print nozzles can become plugged. The required maintenance can cost thousands of dollars annually beyond the cost of replacement parts and the original equipment itself. When a marking system fails, the failure is typically not detected until the boards reach the next machine center, potentially meaning that a hundred or more boards must be physically removed from the process and either reintroduced ahead of the marking system or manually processed.
Marking boards with ink or paint can reduce their value as potential appearance-grade products destined for exposed applications. Boards typically processed through a marking system have been previously planed and are ready for immediate use. Some uses include wall paneling or exposed ceilings and floors. If the final finish will be a non-opaque stain or paint, any non-natural marking will not be acceptable. Furthermore, print media typically contain or are mixed with a fluorescent pigment or dye to provide better contrast to improve mark-reading performance. Such pigments may be invisible in normal lighting, but the marks will glow under an ultraviolet (black light) source. The ultraviolet marks are, therefore, unacceptable for applications where the surfaces are inadvertently illuminated by a lighting source that emits UV light.
While existing board tracking systems may be suitable for some specific purposes, a more universal method for tracking boards, regardless of their condition or their final application, is desirable.